The present invention relates to a mechanism for mounting a heat sink on a multi-chip module.
A multi-chip module which includes a plurality of chips at a high packing density, generally produces a large amount of heat. Accordingly, it is necessary to cool the multi-chip module by some means. Usually, a heat sink is mounted on a module cap with the aid of a screw or the like, to cool the module.
A related art with respect to the structure of the multi-chip module provided with the heat sink is disclosed in, for example, JP-A-60-143,653. This art, however, fails to show how to attach the heat sink to the module. A structure for mounting a heat sink on a multi-chip module, has not yet been established.
Further, another Japanese patent application (Appln. No. Hei 1-101,771) filed by the present assignee, is not which prior art to the present invention discloses a heat sink but does not show how to mount a heat sink on a module.
As mentioned above, a favorable structure for mounting a heat sink on a module, has not yet been established. When the heat sink is bonded to the module by a screw, there arises a problem that the cap plate of the module is required to have thickness greater than a predetermined value. Further, the heat sink is fixed to the cap plate at a plurality of positions by screws, and it is difficult to generate the same fixing force at the above positions. Thus, there arises another problem that it is difficult to surely maintain heat-conductive grease between the heat sink and the cap plate, and to prevent air from being mixed with the grease.
In order to improve the operation speed and reliability of a semiconductor device, it is necessary to make the heat resistance between a heat sink and a module cap, as small as possible. Thus, grease which is high in thermal conductivity, is typically inserted between the module cap and the heat sink. Further, a mechanism for mounting the heat sink on a module is required to allow the deformation of each of the heat sink and the module and variations in dimensions of each of the heat sink and the module. Specifically, in a case where the module cap is made of ceramics having high thermal conductivity such as aluminum nitride, it is difficult to perform a thread-cutting operation for the module cap. Even if the thread-cutting operation can be performed, a crack will readily generate in the module cap at a time the heat sink is fixed to the cap by a screw.